Sensors are commonly used for converting an externally physical quantity into an electric signal, so sensors are used widely in daily life and industry. The related products of sensors includes accelerometers, gyros, resonators, pressure sensors, respiratory sensors, magnetometers, temperature sensors, ambient light sensors, proximity sensors, etc.
A static or dynamic offset is generated by process variation or ambient environment variation of the sensor. For example, FIG. 1 shows a CMOS MEMS sensor chip 10, which is commonly applied to an accelerometer in a mobile phone. The sensor detects differential capacitances between an electrode 11 and adjacent electrodes when the mobile phone performs a relative movement. Hence, theoretically, if the mobile phone does not performs a relative movement, the capacitance between the electrode 11 and one of the adjacent electrodes is equivalent to the capacitance between the electrode 11 and the other adjacent electrodes. That is, in the design of the sensor chip 10, the area and the distances between the electrode 11 and the adjacent electrodes must be the same. However, in the actual process, the areas of each electrode are slightly different, and the distances between any two electrodes may be different. Even though the sensor does not perform a relative movement, differential capacitances occur between the electrode 11 and the adjacent electrodes. This phenomenon is called static offset of the sensor. On the other hand, when the ambient environment (such as temperature) of the sensor is changed, the capacitances between electrodes will be changed. This phenomenon is called dynamic offset of the sensor.
In the prior art, in order to solve the aforementioned problems, a capacitance compensation circuit is employed. FIG. 2 shows a capacitance compensation circuit 20. According to the outputs from the positive and negative output terminals of the sensor, the equivalent capacitance Ceq generated by the capacitance compensation circuit 20 is determined to compensate to the positive terminal or the negative terminal of the sensor. For example, when the voltage outputted by the negative terminal of the pair of differential output terminals of the sensor is greater than the voltage outputted by the positive terminal of the pair of differential output terminals, the equivalent capacitance Ceq will be compensated to the positive terminal of the sensor. However, in order to produce a tiny compensation capacitance, a capacitor network is employed. The capacitor network is configured with various capacitors and various switch elements, so that the capacitance compensation circuit 20 occupies a large area of the sensor chip. Moreover, the capacitance compensation circuit 20 is only constituted by a compensation capacitor array, so that an extra circuit for implementing the calibration algorithm is needed. That is, the capacitance compensation circuit 20 not only occupies large space, but also the minimum compensation value is restricted.